1. Technical Field
This disclosure relates to methods of improving the efficiency of polymerization processes employing multiple reactors. More specifically, this disclosure relates to methods of activating and/or maintaining catalytic activity across a multi-reactor chain for the production of impact copolymers.
2. Background
Synthetic polymeric materials, particularly polypropylene resins, are widely used in the manufacturing of a variety of end-use articles ranging from medical devices to food containers. Commercial grade polypropylenes are typically produced using a Ziegler-Natta and/or a metallocene catalyst in a polymerization process. Many industries, such as the packaging industry, utilize these polypropylene materials in various manufacturing processes to create a variety of finished goods.
Impact copolymers are a rapidly growing segment of the market for synthetic polymeric materials. In contrast to homopolymers, these materials consist of at least two monomers synthesized in such a fashion as to generate a final product having improved mechanical and/or physical properties when compared to the homopolymer. For example, a polypropylene impact copolymer may be synthesized through the additional copolymerization of propylene and ethylene in a secondary reactor downstream of at least one reactor for synthesis of the polypropylene homopolymer. Varying parameters, such as the reaction conditions in the secondary reactor and/or the quantities of comonomer used may allow for the production of a polypropylene impact copolymer tailored to meet the needs of a wide-range of end-use applications. One drawback to the production of impact copolymers is the variation in production process efficiency due to the use of reactor systems comprising multiple types of reactors. Thus, it would be desirable to develop a method of producing impact copolymers having an improved production process efficiency.